Brief description of components

xDrive consists of the following components:

• Transfer case with multi-plate clutch 

  The electronically controlled multi-plate clutch is housed in the transfer case. The multi-plate clutch distributes the drive torque smoothly and as required  between the front and rear axles.

• VTG electric servomotor with incremental sensor and classification resistor 

  The VTG actuator motor opens and closes the multi-plate clutch. The location of the actuator motor shaft and the adjustment rate are detected by the incremental sensor.

  The classification resistor ensures that mechanical tolerances in the transfer case are considered. Optimum function is thus ensured.

• VTG control unit 

  The VTG control unit regulates the locking torque at the multi-plate clutch in the transfer case in response to the following factors:

  • Demand for required locking torque (comes from the DSC control unit)
  • Condition of the transmission oil (calculated in the VTG control unit)
  • Multi-plate clutch wear (calculated in the VTG control unit)
  • Load on VTG actuator motor (calculated in the VTG control unit)
  • Transmission oil temperature (calculated in the VTG control unit)

  The VTG control unit supplies the following information to the DSC control unit:

  • The locking torque currently set
  • All calculated data

  The locking torque is limited whenever needed in order to reduce the frictional work.

• DSC: Dynamic Stability Control 

  DSC 8Plus is installed with the xDrive. With xDrive, DSC includes the following functions:

  • All-wheel control
  • Automatic Differential Brake (ADB-X)
  • Hill Descent Control (HDC)

    All-wheel control 

    Dynamic Stability Control (DSC) specifies the nominal value for xDrive all-wheel control. The nominal value depends on the vehicle's tendency to oversteer or understeer and wheel slip. The nominal value is transmitted to the VTG control unit.

    Signal path: DSC control unit -> Powertrain CAN -> VTG control unit

    Automatic differential brake 

    The automatic differential brake (ADB-X) simulates the function of conventional limited-slip differentials by selectively applying brakes on individual wheels (known from the E53 and the E83).

    Whenever a wheel displays a tendency to spin the ADB-X automatically brakes it down to a preset slip. This effect of this is to increase the drive torque on those wheels that are on a higher-friction surface.

    Hill Descent Control 

    Hill Decent Control (HDC) is a cruise control on four-wheel drive cars for driving downhill (known from the E53 and the E83).

    HDC can be activated and deactivated with a separate button.

    When the HDC button is pressed, HDC automatically reduces road speed. The brakes are applied on all four wheels to reduce road speed to just above walking pace. HDC holds this speed constant (all DSC functions remain active).

    The car's road speed can be freely varied within fixed values by pressing down on the accelerator pedal, brake pedal or the buttons for the cruise-control system.

The following control units and switches are incorporated in xDrive functions:

• DME or DDE: Digital engine electronics or digital diesel electronics 

  The DME or DDE modifies the engine response as required by the DSC control unit (such as power reduction to prevent the driven wheels from spinning).

• Instrument cluster display 

  System states are displayed as follows:

  • DSC indicator and warning light lights up:

    DSC/xDrive not activated

  • DSC indicator and warning light lights up and acoustic signal:

    DSC defective, ABS not affected, VTG control unit OK

    or

    DSC OK, VTG control unit defective

    -> All-wheel drive in emergency mode

  • DSC indicator and warning light, ABS indicator and warning light and general brake warning lamp light up and acoustic signal:

    Total failure of the DSC and/or malfunction of the VTG control unit

  -> All-wheel drive in emergency mode

• CAS: Car access system 

  CAS provides input signals relating to terminal voltage (e.g. terminal 15 ON).

• SGM or KGM: Safety and gateway module or body-gateway module 
  • E60, E61

  The KGM replace the SGM as from 09/2005.

  SGM: The module is the data interface (= gateway) between the K-CAN, PT-CAN and byteflight.

  KGM: The module is the data interface (= the gateway) between the K-CAN and the PT-CAN.

• JBE: Junction box electronics 
  • E90, E91, E92

  The JBE is the data interface (= the gateway) between the K-CAN and the PT-CAN.

  The junction box consists of the JBE and the power distributor. The power distributor supplies power to the VTG control unit.